Direct current supply system



Nov. 24, 1942. 1 MALLlNG 2,302,876

DIRECT CURRENT SUPPLY SYSTEM Filed April 4, 1941 TELEVISION RECEIVER ATTORNEY Patented Nov. 24, 1942 DIRECT CURRENT SUPPLY SYSTEM Leonard R. Malling, Donglaston, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application April 4, 1941, Serial No. 386,823

8 Claims.

The present invention relates to direct current supply systems and, particularly, to powersupply systems of the type which use a vacuumtube oscillation generator to derive a high unidirectional potential from a relatively low po tential supply circuit. While the invention is of general application, it has particular utility as the power-supply system for a cathode-ray type of image-reproducing tube conventionally used in television receivers and the invention will be described in that connection.

The present day television receivers commonly use a cathode-ray type of image-reproducer tube which requires energizing potentials of the order of five thousand to ten thousand volts. Such high potentials may be derived from the relatively low voltage alternating current power-supply mains, but this requires relatively expensive, heavy, and generally bulky transformers, rectifiers, and filters and involves a considerable shock hazard.

It has been proposed that the high energizing potentials for such cathode-ray tubes be derived from a relatively low voltage supply circuit by the use of a vacuum-tube oscillation generator. This generator may be the scanning generator conventionally used with cathode-ray tubes or may be a separate generator provided especially for the high voltage supply. High voltage supplies of this nature heretofore have had the disadvantage of relatively poor voltage regulation; that is, the energizing voltage applied to the cathode-ray tube has been materially higher during the time when an over-all dark picture was reproduced than was the case when an over-all relatively light picture was reproduced. It has been proposed that the regulation be improved by connecting across the output of such powersupply system a load impedance for so loading the system that the normal variations of load caused by the operation of the cathode-ray picture tube was only a small percentage of the total load on the power-supply system. This load impedance generally comprised a number of resistors serially-connected across the output of the supply system. The arrangement has the disadvantages that the resistors must be made to withstand the high voltage required to energize the cathode-ray tube and must be well insulated from ground by high voltage insulation. Additionally, this method of regulation has the disadvantages that the resulting regulation is not all that could be desired and is wasteful of power in that only a small percentage of the total output of the supply system is useful to energize the cathode-ray picture tube.

It is an object of the present invention, therefore, to provide a new and improved high voltage direct current supply system and one which avoids one or more of the disadvantages and limitations o. the prior art systems.

It is a further object of the invention to provide a high voltage direct current supp y System having high efiiciency and good regulation and one in which the regulation is accomplished in a new and improved manner.

It is an additional object of the invention to provide a high voltage direct current supply system of the type which uses a vacuum-tube oscillation generator to derive a high unidirectionalpotential output from a relatively low potential input wherein a well regulated output is obtained.

In accordance with one embodiment of the invention, a high voltage direct current supply system for a variable-impedance load circuit comprises a low-voltage supply circuit, an oscillation generator coupled to said supply circuit, and means for deriving from the generated oscillations a high voltage unidirectional potential tending to vary with impedance variations of the load circuit and for applying the derived potential thereto. The system includes means for maintaining substantially constant the magnitude of the potential applied to the load circuit, comprising means responsive to the current therethrough for controlling the oscillation generator.

in accordance therewith to compensate the tendency of the potential to vary.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring now to the drawing, the single figure thereof is a circuit diagram, partly schematic, of a complete television carrier-signal receiver embodying the direct current supply system of the present invention in a preferred form.

Referring more particularly to the drawing, in general the television receiver l0 has an input circuit connected to an antenna system I I, I2 and has an output circuit connected to the input electrodes comprising a control electrode l3 and a cathode 14 of a cathode-ray type of image-reproducer tube I5. The television receiver [0 pref erably is of the superheterodyne type and includes radio-frequency, intermediate-frequency, and video-frequency amplifiers, a detector, and linescanning and field-scanning generators coupled to the seaming windings 15 of the cathode-ray tube l5. The cathode-ray tube I5 includes a first anode l1 and a second anode I8 which are energized from a high voltage direct current powersupply system I9, more fully described hereinafter.

It will be understood that-the apparatus just described may. with the exception of the powersupply system I9, be of a conventional construction and operation, the details of which are well known in the art, rendering a detailed descriptionthereof unnecessary. Considering briefly the operation of the receiver as a whole, and neglecting for the moment the operation of the power-supply system I9, presently to be described, the television receiver I selects a desired television carrier signal, amplifies it at radio frequency, converts it to an intermediatefrequency carrier signal which is further amplifled and subsequently detected to derive the modulation components thereof. The picture signalmodulation components are further amplified by the video-frequency amplifier of unit It and are applied to the input electrodes of the cathoderay tube I to modulate the cathode-ray beam thereof. The synchronizing-signal components of the television signal are separated and applied to the scanning generators of unit I0 to synchronize the operation thereof. generators supply scanning currents through the deflecting windings I6 thereby to deflect the signal-modulated cathode-ray beam of tube I5 in two directions normal to each other to reproduce the television image on the screen of tube I5. During this operation, the several electrodes of tube I5 are energized at suitable operating potentials applied thereto from the power-supply system I9.

Referring now more particularly to the portion of the system embodying the present invention, the power-supply system I9 includes an oscillation generator comprising a vacuum tube having a space-charge grid 2| and means for coupling the input and output electrodes thereof comprising an oscillation transformer 22 having coupled windings 23, 24 which are respectively connected to the input and output electrodes of vacuum tube 20. The oscillation transformer 22 is provided with a tertiary winding 25 which is coupled to the winding 24 to derive relatively high voltage oscillations from the oscillations developed in winding 24. The winding 25 is coupled to means for deriving from the generated oscillations a high-voltage unidirectional potential comprising a series-connected diode rectifier device 26 and a load circuit including a filter condenser 21 in parallel with odes I1, I8 of the cathode-ray tube I5 so that there is applied between these electrodes and the cathode electrode I4 suitable unidirectional potentials derived across the condenser 21 by rectification of the oscillations generated by vacuum tube 20. v

The anode circuits of cathode-ray tube I5 effectively constitute a variable-impedance load device, the average impedance thereof varying with the average or background value of the video-frequency signal applied to the control electrode I3 from the television receiver Ill. The magnitudes of the unidirectional potentials applied to the electrodes of tube 15 from the power-supply system I9 tend undesirably to vary with such impedance variations and there is, therefore, provided in the power-supply system l9 means for maintaining substantially constant ;he magnitude of the potentials circuits of the an- The scanning applied to the electrodes of tube l5 comprising means responsive to the currents of the anodes I1 and I8 of tube I5 for varying the bias of the space-charge grid 2I of vacuum tube 20 in accordance therewith to compensate the tendency of the derived unidirectional potentials to vary. This means comprises an impedance including a voltage-divider resistor 28 connected between the cathode I 4 of tube I5 and ground anda vacuum-tube repeater 30 having input electrodes including a control electrode 29 which is coupled across a selectable portion of the voltage divider 28 through the adjustable contact thereof. This impedance, which is in'circuit with the load circuit of tube I5, is utilized to develop a control potential from the current therethrough. The

cathode circuit of vacuum tube 30 forms the output circuit thereof and includes a cathode impedance, comprising a serially-connected voltage-divider resistor 3I and fixed resistor 32,

across which there is developed a control potential the magnitude of which varies with the anode current of tube I5. The adjustable contact of the voltage divider 3| is connected to the spacecharge grid H of vacuum tube 20 to vary the bias thereof with variations of the space current of vacuum tube 30. The voltage divider 3| and its adjustable contact are, therefore, included in a means for applying a selectable portion of the control potential to the, grid 2I to compensate the tendency of the unidirectional potential to vary. The vacuum tubes 20 and 30 are energized by a low-voltage supply circuit which includes a source of space current indicated as +3. The source of space current +B is also connected through a voltage-divider resistor 33 and the resistor 32 to ground. The adjustable contact of the voltage divider 33 is connected to the cathode of vacuum tube 20 to provide a flxed bias for the space-charge grid 2I. The vacuum-tube repeater 30 is, therefore, included in a means responsive to the current through tube I5 for controlling the oscillation generator 20 in accordance therewith to compensate the tendency of the unidirectional potential to vary with impedance variations of the load circuit.

In considering the operation of the circuit just described, it will be assumed that the television signal applied from the television receiver ID to the control electrode I3 of the cathode-ray tube I5 is such that the fluorescent screen of tube I5 remains darkened over several consecutive picture frames. The cathode-ray beam of tube I5 is now extinguished and the anodes I'I, I8 of tube I5 draw no space current from the supply system I9. No potential is, therefore, developed across the voltage divider 28 and the control electrode 29 of the vacuum-tube repeater 30 is biased only by the potential developed across the voltage divider 3| and cathode resistor 32. The space current of tube 30 is a minimum under these conditions and the bias applied tothe space-charge grid 2| of vacuum tube 20, this bias being the sum of the selected portion of the steady bias developed across the voltage divider 33 and the selected portion of the control potential developed across the voltage divider 3|, has a large negative value. The vacuum tube 20 generates oscillations of sinusoidal wave form and of frequency determined by the inductance and distributed capacitance of the windings of transformer 22. The amplitude of the oscillations generated by vacuum tube 20 varies inversely with the bias of the space charge grid 2I so that the generated oscillations have a predetermined minimum amplitude under these conditions. The oscillations are peak-rectified by the rectifler device 26 to develop a unidirectional potential of predetermined magnitude across the condenser 21 which is applied to the anodes I1 and I8 of cathode-ray tube IS. The constants of the transformer 22 are preferably so chosen that the frequency of the generated oscillations is high. This minimizes the required capacitance of the filter condenser and allows the use of a relatively small filter condenser 21, which is desirable from the standpoint that a small filter condenser ensures minimum energy storage therein and consequently minimizes the hazard of electrical shock by accidental contact with a circuit containing the high unidirectional voltage derived by the power-supply system l9.

Now assume that the television signal which is applied to the control electrode I3 of the cathode-ray tube I5 is such that the screen of tube I5 is brightly illuminated over several consecutive picture frames. The space current supplied by the supply system l9 to the anodes l1 and I8 of tube I5 is now large and the potential developed across the condenser 21 tends to drop due to a natural regulation characteristic of the oscillation generator including the transformer 22, 24, 25 and that of rectifier 26. At this time, however, a unidirectional control potential is developed across the voltage divider 28 by the space current of tube l5 and this potential has such polarity-that the negative bias of the control electrode 29 of tube 3|! is reduced. The anode current of this tube consequently increases to increase the unidirectional control potential developed across the voltage divider 3|. An increase of the latter potential reduces the negative bias applied to the space-charge grid 2| of the vacuum tube 20. The amplitude of the oscillations generated by vacuum tube 20 thereupon tends to increase with a resulting increase in the magnitude of the unidirectional potential developed across the condenser 21. By proper adjustment of the adjustable contacts of the voltage dividers 28, 3|, and 33, this tendency of the amplitude of the generated oscillations to increase with decreasing bias applied to the grid 2| may be made to just compensate for the tendency of the unidirectional potential developed across the condenser 21 to decrease with the increased value of space current consumed by tube l5 from the supply system iii. The potentials applied to the anodes l1 and iii of the cathoderay tube l5, therefore, remain substantially constant in magnitude over the wide range of variations of loading of the power-supply system l9 resulting from the normal operation of the oathode-ray tube l5.

Thus, the vacuum tube 30 comprises means responsive to the control potential developed across the voltage divider 28 for varying the bias of the space-charge grid 2| of vacuum tube 20 in accordance therewith to compensate the tendency of the unidirectional potential developed across the condenser 21 to vary with the impedance of the anode-cathode space current path of the cathode-ray tube IS. The vacuum tube 30 is, therefore, included in a means which is responsive to the control potential for varying the power output of the oscillation-generating means 20 in accordance with the control potential to compensate the tendency of the unidirectional potential to vary. The space-charge grid 2| of tube 20, on the other hand, comprises means responsive to the control potential developed in the output circuit of vacuum-tube repeater 30 for varying the amplitude of the oscillations generated by tube 20, and thereby the power output of the latter, in accordance with variations of such control potential to compensate the tendency of the developed unidirectional potential to vary.

While the power-supply system of the invention has been described as including a vacuumtube oscillator individual thereto, it will be evident that the oscillation generator of the supply system may comprise one of the scanning generators of the television carrier-signal receiver HI, preferably the line-scanning generator thereof. In this event, the vacuum-tube re peater 30 of the supply system l9 controls the bias of any control electrode of the scanning gen- .erator vacuum tube which is effective to control the transconductance of the latter tube.

From the foregoing description of the invention, it will be evident that a high voltage direct current power-supply system embodying the invention not only has the advantage of a higher degree of efliciency than that heretofore attainable by prior art supply systems of this nature utilizing loading resistors, but has the additional advantage that the power-supply system has a well regulated output characteristic.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A high voltage direct current supply system for a variable-impedance load circuitpomprising, a low voltage supply circuit, an oscillation generator coupled to said supply circuit, means for deriving from said generated oscillations a high voltage unidirectional potential tending to vary with impedance variations of said load circuit and for applying said potential thereto, and means for maintaining substantially constant the magnitude of said potential applied to said load circuit comprising means responsive to the current therethrough for controlling said generator in accordance therewith to compensate said tendency of said potential to vary.

2. A high voltage direct current supply system for a variable-impedance load circuit comprising, a vacuum tube having a grid, means including said vacuum tube for generating oscillations, means for deriving from said generated oscillations a high voltage unidirectional potential tending to vary with impedance variations of said load circuit and for applying said potential thereto, and means for maintaining substantially constant the'magnitude of said potential applied to said load circuit comprising means responsive to the current therethrough for varying the bias of said grid in accordance therewith to compensate said tendency of said potential to vary.

3. A high voltage direct current supply system for a variable-impedance load circuit comprising, a vacuum tube having input and output electrodes and a space-charge grid, means for coupling said input and output electrodes to generate oscillations, means for deriving from said generated oscillations a high voltage unidirectional potential tending to vary with impedance variations of said load circuit and for applying said potential thereto, and means for maintaining substantially constant the magnitudeoi' said potential applied to said load circuit comprising means responsive to the current ther ethrough for varying the bias of said space-change grid in accordance therewith to compensate said tendency of said unidirectional potential to vary.

4. A high voltage direct current supply system for a variable-impedance load circuit comprising, a vacuum tube having a grid, means including said vacuum tube for generating oscillations, means for deriving from said generated oscillations a high voltage unidirectional potential tending to vary with impedance variations of said load circuit and for applying said potential thereto, and means for maintaining substantially constant the magnitude of said potential applied to said load circuit comprising an impedance in circuit with said load circuit for developing a control potential from the current therethrough, and means responsive to said control potential for varying the bias of said grid in accordance therewith to compensate said tendency of said unidirectional potential to vary.

5. A high voltage direct current supply system for a variable-impedance load circuit comprising, means for generating oscillations, means for deriving from said generated oscillations a high voltage unidirectional potential tending to vary with impedance variations of said load circuit and for applying said potential thereto, means for maintaining substantially constant the magnitude of said potential applied to said load circuit comprising an impedance in circuit with said load circuit, a vacuum-tube repeater having input electrodes coupled to said impedance and having an output circuit in which there is developed a control potential the magnitude of which varies with the current through said load circuit, and means responsive to said control potential for varying the power output of said oscillation-generating means in accordance therewith to compensate said tendency of said unidirectional potential to vary.

6. A high voltage direct current supply system for a variable-impedance load circuit comprising, means for generating oscillations, means for deriving from said generated oscillations a high voltage unidirectional potential tending to vary with impedance variations of said load circuit and for applying said potential thereto,

means for maintaining substantially constant the magnitude of said potential applied to said load circuit comprising a resistor in circuit with said load circuit, a vacuum-tube repeater having input electrodes coupled to said resistor and having a cathode impedance across which there is developed acontrol potential the magnitude of which varies with the current through said load circuit, and means responsive to said control potential for varying the amplitude of the oscillations generated by said generating means in accordance therewith to compensate said tendency of said unidirectional potential to vary. I

7. A high voltage direct current supply system comprising, a vacuum tube having a grid, means including said vacuum tube for generating oscillations, a cathode-ray tube having anode and cathode electrodes, rectifying means coupled to said generating means for deriving from said generated oscillations a high voltage unidirectional potential and for applying said potential between said anode and said cathode electrodes, the magnitude of said potential tending undesirably to vary with the anode currentof said cathode-ray tube, means for maintaining substantially constant the magnitude of said potential applied to said anode comprising a resistor in circuit with said anode and cathode, a vacuum-tube repeater having input electrodes coupled across a selectable portion of said resistor and having a cathode resistor across which there is developed a control potential the magnitude of which varies with the anode current of said cathode-ray tube, and means for applying a selectable portion of said control potential to said grid to compensate said tendency of said unidirectional potential to vary.

8. A high voltage direct current supply system for a variable-impedance load circuit comprising, a vacuum tube having a grid, means including said vacuum tube for generating oscillations, means for deriving relatively high voltage oscillations from said generated oscillations, means including a filter condenser for rectifying said high voltage oscillations to derive a high voltage unidirectional potential tending to vary with impedance variations of said load circuit and for applying said potential thereto, the frequency of said generated oscillations being high to minimize the required capacitance of said filter condenser, thereby to reduce the hazard of electrical shock by accidental contact with said derived high voltage, and means for maintaining substantially constant the magnitude of said potential' applied to said load circuit comprising means responsive to the current therethrough for varying the bias of said grid in accordance therewith to compensate said tendency of said potential to vary.

LEONARD R. MALLING. 

